Magnetic switching apparatus for reducing contact bounce



Jan. 12, 1965 J. E. WALLACE 3,1 6

MAGNETIC SWITCHING APPARATUS FOR REDUCING CONTACT BOUNCE Filed Dec. 21,1962 I 1s d i 15%: n

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TIME (MICROSECONDS) 4 VOLTS FIG. 2b

1 TIME (MICROSECONDS) INVENTOR JOSEPH E. WALLACE AT ORNEY United StatesPatent 3,165,608 MAGNETIC SWITCHING APPARATUS FOR REDUCING CONTACTBQUNCE Joseph E. Wallace, Endicott, N.Y., assignor to InternationalBusiness Machines Corporation, New York, N.Y., a corporation of New YorkFiled Dec. 21, 1962, Ser. No. 246,604 4 Claims. (Cl. 200-87) Thisinvention relates generally to electrical relays and more particularlyto enclosed reed switches operated by circumferential energizing coils.

The usual magnetic reed switch comprises a pair of spaced, overlapping,magnetic reeds supported in cantilever fashion in the opposite ends of asealed glass tube about which is provided an exciter or energizing coil.Current flowing through the coil produces a magnetic flux field whichattracts the free ends of the reeds toward each other and completes theconduction path from one reed to the other. The reeds are made of thin,relatively flexible magnetic material with an air gap of a fewthousandths of an inch between the free ends to permit high speed switchoperation. The reed contacts are sealed free of contaminants to provideexcellent operational reliability.

These switches, however, are subject to contact bounce, which occursWhen the attracted reeds strike each other, resulting in decreased lifeand a delay in useful time during which the contacts are made. Becauseof this difiiculty, structural refinements have been made heretofore toprovide a switch having reduced bounce. These refinements have includeddecreasing reed size, adding an auxiliary contact and reed to theprincipal reeds, providing special coils and changing the gap betweenthe reeds. Such modifications have improved the bounce characteristicbut resulted in a reduction of current capacity, increased manufacturingand assembly costs because of additional elements, or a significantincrease in operating time due to larger mass.

It is, therefore, an object of this invention to provide an improvedreed switch which substantially reduces contact bounce withoutmodification to the reeds.

Another object of this invention is to provide a relatively simple andinexpensive reed switch having little or no contact bounce.

Still another object of this invention is to provide a magneticallyoperated reed switch in which the kinetic energy of approaching reeds issignificantly reduced at the instant of impact.

A further object of this invention is to provide a magnetically operatedreed switch which includes a fixed limit stop for one of the twoapproaching reeds operable to arrest or reverse the motion of one of thereeds prior to imp-act of the reeds.

In accordance with the foregoing objects, this invention provides afixed stop secured in the switch enclosure adjacent one of the magneticreed cantilevers and spaced therefrom less than half the gap between theoverlapping cantilever contacts when the latter are in a d e-energizedposition. When a magnetic fiux field is applied, each reed moves towardthe other to minimize reluctance. One reed is arrested by the stop,however, before impact with the remaining reed so that its approachvelocity reaches zero and then becomes a negative value as it reboundsfrom the stop while being overtaken by the remaining moving reed.

This arrangement eliminates special forming or shaping of the reeds andavoids the addition of auxiliary reeds or electrical contact areas ofthe principal reeds. Less kinetic energy at impact time also prolongsthe life of the contact area.

The foregoing and other objects, features and advan- 3,165,608 PatentedJan. 12, 1965 tages of the invention will be apparent from the followingmore particular description of a preferred embodiment of the invention,as illustrated in the accompanying drawings, wherein:

PEG. 1 is a sectional side elevation view of an electromagnetic reedswitch constructed in accordance with the invention; and

FIGS. 2a and 2b are comparative oscillographic diagrams illustrating thecontact action in reed switches which respectively do not and do embodythe invention.

Referring to FIG. 1, reeds l0 and 11 of a suitable ferromagneticmaterial, such as a nickel-iron alloy, are supported in substantiallyparallel planes as cantilever beams in the opposite ends of a sealedglass enclosure 12 encircled by an energizing electromagnetic coil 13(shown in phantom). Reeds 10 and 11 each have approximately equalmovable lengths from hinge points 14, and their respective free ends 15and 16 overlap and are spaced from each other a predetermined distanceto provide a gap which is usually a few thous-andths of an inch. Thespacing depends on the current requirement, voltage and operating timeof the particular circuit in which the reed switch is used. The reedends may each be plated with a suitable material at the contact area toimprove the electrical connection.

Also secured in the end of enclosure 12 adjacent reed 10 and extendingapproximately parallel to the reed as a cantilever is a member 17 havingan upturned end 18 which serves as a stop to limit the downward movementof reed 10. End 13 is preferably positioned near the contact area tominimize the whipping action upon impact between reed 10 and end 18. Theend of the stop member has a substantially flat surface which is spacedfrom reed 10 at a distance less than half the gap between ends 15 and16. This spacing will vary according to the distance end 18 is locatedfrom the reed gap.

Member 17 has a relatively large mass compared to reed 10 so that itpresents a substantially rigid stop for the reed. The stop member 17 ispreferably a hardened non-magnetic material to reduce wear and to avoidany effect upon the make or break time of the reeds.

In operation, coil 13 is supplied with current which establishesmagnetic flux lines passing through reeds 10 and 11. The reeds movetoward each other with approximately equal acceleration and velocity todecrease the magnetic reluctance of gap. While reed 11 continues movingtoward reed 10, reed 10 strikes the stop surface of end 18 so that itsmovement is arrested. Because of the kinetic energy of reed 10 andrelative inflexibility of member 17, the reed rebounds and moves awayfrom approaching reed 11. The latter reed, however, is moving at ahigher velocity and overtakes reed 10. The result is that ends 15 and 16make contact at low relative velocity with a low impact energy becausethey are traveling in the same direction when impact occurs.

The contact action of the reed switch described above is illustrated bycomparing the volt-age versus time oscillograms of FIGS. 2a and 2b,obtained in actual comparative tests. These figures show the voltagedrop across a load resistor in series with the switch contacts. FIG. 2arepresents the reed switch action without a stop, while FIG. 2brepresents the switch closure using stop member 17 positioned as shownin FIG. 1. In this comparative example, coil 13 having a winding of10,000 turns of No. 42 wire and 1600 ohms resistance was energized withtwelve volts D.C. Free ends 15 and 16 of the reeds were spaced .003 inchand the stop surface of end 18 was spaced .001 inch from the undersideof reed 10.

As seen in FIG. 2a, the switch contacts first closed after approximately560 microseconds (,uS.) after coil energization and then opened againapproximately ,uS. later because of bounce. However, when the stopmember was installed, switch closure occurred approximately 700 s. aftercoil energization with no subsequent bounce. Thus, theaddition of stopmember 17 eliminated contact bounce and prevented the production ofextraneous pulses in the switch circuit. This permits the immediateutilization of the switch circuit without the necessity of a delay tolet the switch contacts stabilize.

End 18 of he stop member is preferably positioned from reed It at lessthan half the gap between the free ends of the reeds. This assures that,when the coil is energized, reed it) will start its rebound from thestop before the reeds seal. If the stop is positioned too close to reedit the reed will have become stationary before impact by end 16 of reed11 so that operating time will increase and bounce will occur.

While 'the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:

1. An electrical switching device comprising:

a pair of resilient overlying contact elements formed of magneticmaterial and cantilever supported at their remote ends and separated bya gap at their adjacent velocities causing the elements to establishelectrical connection substantially without contact bounce. 2. Anelectromlagnetically controlled switching device comprising: a

a pair of overlying cantilever supported resilient contact elementsformed, of magnetic material and separated by a gap; a coil energizableto cause both said elements to move toward and into contact with eachother; and means providing a stop surface engageabie by one of saidelements during energization of said coil and located from said oneelement a distance less than half the said gap, such that said oneelement will strike said step and be rebounding therefrom at the instantit is overtaken and contacted by said other element, thereby tosubstantially reduce impact sinetic energy and minimize bounce of thecontactproviding elements. 3. A switching device according to claim 2,wherein the stop surface is disposed adjacent the unsupported end ofsaid other element, and both said elements and the stopsurface-providing means are sealed within a common:

enclosure.

4. A switching device according to claim 2, wherein said elements aresubstantially parallel in the absence of said magnetic field and aresupported to have substantially equal movable lengths.

References Cited in the file of this patent UNITED STATES PATENTS2,535,400 Ellwood Dec. 26, 1950 3,025,371 Medal Mar. 13, 1962 FOREIGNPATENTS 1,237,011 France June 13, 1960

1. AN ELECTRICAL SWITCHING DEVICE COMPRISING: A PAIR OF RESILIENTOVERLYING CONTACT ELEMENTS FORMED OF MAGNETIC MATERIAL AND CANTILEVERSUPPORTED AT THEIR REMOTE ENDS AND SEPARATED BY A GAP AT HTEIR ADJACENTENDS; MEANS FOR PRODUCING A MAGNETIC FIELD FOR EFFECTING MOVEMENT OFSAID ELEMENTS TOWARD EACH OTHER; AND MEANS PROVIDING A STOP SURFACEENGAGEABLE BY ONE OF SAID ELEMENTS UPON CREATION OF SAID MAGNETIC FIELD,SAID SURFACE BEING DISPOSED SO AS TO BE ENGAGED BY SAID ONE ELEMENTBEFORE SAID ELEMENT CONTACT EACH OTHER, WHEREBY AT THE INSTANT SAIDELEMENTS COME INTO MUTUAL CONTACT, BOTH SAID ELEMENT WILL BE MOVING INSUBSTANTIALLY THE SAME DIRECTION BUT AT DIFFERENT VELOCITIES CAUSING THEELEMENTS TO ESTABLISH ELECTRICAL CONNECTION SUBSTANTIALLY WITHOUTCONTACT BOUNCE.